The present invention relates to a ram-type packer element for use in a blow-out protector and, more particularly, to a packer element which is designed to be useful as a stripping tool and provide good shear-resisting properties.
Blow-out protectors are well known. In general, they are valve devices which are designed to pack off the annular space between the drill pipe and the well casing in the event of a blow-out. A typical blow-out protector comprises, as its essential components, a packing element and an exteriorly operated actuator means which acts on the packing element and forces it into sealing engagement with the drill pipe. Usually, the blow-out protector includes or is associated with some means of sensing or reacting to an increase of pressure in the well hole and is designed such that the protector is actuated and the well pressure is controlled before the well pressure can do substantial damage to the drilling equipment or cause injury at the drilling site.
One example of a blow-out protector is illustrated in U.S. Pat. No. 2,231,221. In that protector, the packing element is carried on an elongated actuator sleeve provided with a plurality of annular gear teeth. In the event of a blow-out, the packing element is driven by the sleeve into abutment with a shoulder located internally in the well hole whereupon the packing element is compressed and the packing extrudes or bulges from the element and into sealing engagement with the drill pipe. There are numerous other examples of blow-out protectors in the art which differ in the design of the packing element and the means whereby the element is forced into sealing engagement with the drill pipe. A few examples of the other drill pipe protectors that have been known are disclosed in U.S. Pat. Nos. 2,375,432; 2,139,526; and 1,963,683.
A frequent design used for the packing element, or "gate" as it is sometimes referred, is a generally semi-circular structure in which an elastomeric packing is interposed between two semi-circular reinforcing elements. The structure is formed with a semi-cylindrical cut out or arch in its diametric side which receives the drill pipe. The packing which faces on this cut out defines a work surface which packs off the well casing. The elastomeric packing is usually a block of a high strength wear-resistant rubber compound. Packing elements are used in pairs with one element positioned diametrically opposite the other on each side of the drill pipe such that the drill pipe extends through the circular aperture formed by the interfacing semi-cylindrical arches. In the blow-out protector, the elements function as a packer valve. Pressure is applied to each element of the pair whereby the element is compressed or deformed and the packing extrudes from the element and engages the drill pipe to seal off the annular space around the pipe in the well.
One problem which blow-out protector packer elements have faced is a tendency for the elements to wear out and fail in use. A major source of wear occurs when the drill pipe is pulled out of the well to replace damaged pipe or a worn drill bit. As the drill pipe is withdrawn from of the well, it is coated with the drilling fluids which carry suspended bits of cut rock and the like. As the surface of the pipe slides across the packing element in the blow-out protector, the packing element is subjected to elongational shear along the working face. This forceably elongates the working surface and gradually mechanically degrades the packing element to the point that it can no longer function satisfactorily. One practice that is frequently adopted which intensifies abrasion and wear is to partially close the blow-out protector as the drill pipe is removed from the well in order to use the packing element as a stripping tool to remove mud and drilling fluids from the drill pipe surface. This operation prevents even greater abrasion and wear problems since the packing element is positively biased against the surface of the drill pipe as it is removed. Under the applied pressure of the blow-out protector, the packing element is subjected to higher shearing forces which enhances mechanical degradation. As the packing element is worn and degraded it becomes unable to deliver a uniform sealing action around the circumference of the drill pipe in the event of a blow-out.
Several attempts have previously been made to overcome the wear-resistance and abrasion-resistance problems and to improve the useful service life of blow-out protector packing elements. Efforts have particularly concentrated on developing elastomeric compositions and elastomeric composites which resist the wear and abrasion caused by the drill pipe. Relatively little attention has been directed to the packing element design itself.